1. Field of the Invention
The invention relates to an internal combustion engine.
2. Description of Related Art
A technique for generating a swirl flow in an axial direction of a cylinder of an internal combustion engine, that is, a so-called tumble flow in the cylinder of the internal combustion engine has conventionally been known. When the tumble flow is generated in the cylinder, mixing of intake air and fuel is promoted, and consequently, combustibility in the internal combustion engine can be improved.
In addition, Japanese Patent Application Publication No. 8-74584 (JP 8-74584 A) discloses such a configuration that an intake port is formed as a straight port that extends straight and obliquely downward toward a combustion chamber from a side surface of a cylinder head while an inner diameter thereof remains the same in an internal combustion engine in which a tumble flow is generated in a cylinder. In this configuration described in JP 8-74584 A, an inner surface of an opening hole of a valve seat in the intake port that is opened to the combustion chamber is formed to have a conical surface that has a larger inner diameter than the intake port and is enlarged toward the combustion chamber. In addition, a portion of the conical surface is formed to substantially correspond to a ceiling surface of the intake port.
In Japanese Patent Application Publication No. 2004-316609 (JP 2004-316609 A), in an internal combustion engine that includes an intake port for introducing the intake air in a manner for the intake air to be biased to one side of a cylinder with respect to a center line of the cylinder, so as to generate a tumble flow in the cylinder, a configuration is disclosed in which a step projected to an inner side of the intake port is provided on a boundary between a wall surface among wall surfaces of the intake port that is on a far side from the one side and a throat of a valve seat that continues from the intake port.
In Japanese Utility Model No. 2532417, a configuration in which a cross-sectional shape of an intake port that is a linear straight port is formed as an oval shape or a substantially rectangular shape is disclosed.